Reimbursement of telephone charges for calls made during the course of your employment would be a legitimate expense and would not attract taxation.
Reimbursement of private calls made from your own home telephone would be considered a benefit by HM Revenue and Customs and would be subject to their formula for calculating the appropriate 'cost of benefit', which is taxable.
There is no charge to tax on:
- one mobile phone provided to an employee, or
- any line rental or the cost of any private calls for that phone paid for by the employer, unless these can be converted into money by the employee.
The rules and regulations are complex and further advice can be sought from your local tax office.